Electronic flash unit



May l5, 1962 B. L. FRIEDMAN ELECTRONIC FLASH UNIT 2 Sheets-Sheet 1 Filed July 17, 1957 (SAPAC/TOR Oy/l \2 BERNnR D L POWER S (IP/LY SENS/N6 ELEMEA/ 7' May 15, 1962 B. l.. FRIEDMAN 3,035,219

ELECTRONIC FLASH UNIT y Filed July 17, 1957 2 Sheets-Sheet 2 CAPAC CAPC AAAA

CAPAC.

LOAD

INVENTOR. BERNaRp L FRIEvMaN HS @17mm-ELL States The present invention relates to an electronic Hash unit and more particularly to a means and method of rapidly charging capacitors used as a power source for photography iiash lamps and the like and to a means for carefully and precisely controlling the voltage applied to the systern.

In conventional Hash units a power source is connected across a capacitor and the capacitor is charged to the level of the source voltage. When desired, the capacitor is then discharged through the Hash lamp unit causing a brilliant Hash of short duration with the brilliance of the Hash dependent upon voltage on the capacitor and the other parameters of the circuit. After the Hash is completed the capacitor is again recharged to a selected level. Because the luminescence of the lamp should be accurately and uniformly controlled in order to obtain uniform and desired results, it is important to charge the capacitor to a consistent and precise level. Moreover, as these Hash units may be used repeatedly within short intervals of time, it is also essential to provide a system in which the capacitor may be charged rapidly.

It is, therefore, an object of the present invention to provide a system in which a more rapid charge of a capacitor used to illuminate a Hash lamp may be obtained.

It is also an object of the present invention to provide` means for maintaining a precise Voltage on the capacitor or capacitor banks when not being discharged through the lamp.

Further objects of the present invention include the pro- .vision of a simplified electronic circuit adapted to minimize the voltage required to maintain the capacitor at a lselected level.

In the conventional system as described above, the voltvage across the capacitor at any given time may be deterthe source voltage, C equals the capacity of the capacitor or capacitors in microfarads, t equals the time interval during which the source delivers charge to the condenser, and R equals the total impedance of the circuit including source impedance, circuit resistance and internal impedance of the capacitor.

It is clear, therefore, that in conventional design the capacitor will charge at an exponential rate in which the capacitor will charge to 63% of the source voltage in the tirst time constant, 63 of the remaining in its second time constant and so on, where the time constant is represented as RC. It will, therefore, take approximately tive time constants for the voltage across the condenser to rise to substantially 100% of the source voltage. In order to reduce this time, it is necessary to make R as small as possible as the size of the capacitor C cannot be reduced with- .out actually decreasing the light output of the unit. There is, however, a practical limitation beyond which the irnpedance cannot be reduced due to Various factors which include size, cost, Weight and the circuit impedance itself.

yIn order to effectively and further reduce the time during which the capacitor is charged to its maximum level, the present invention is designed to elfectively increase the value of E, and in conjunction therewith utilizes a circuit in which the source of this charging voltage E is cut oi at the specified rated level of the capacitor and the circuit is automatically cut into a precisely controlled alternate source of voltage design-ed to maintain the capaci' arent ice itor at a selected level. Under these circumstances in which E is materially increased, the voltage V will increase proportionately in such a manner that the capacitor will charge in a fraction of the time it would normally take with a conventional circuit.

These and other objects and advantages of the present invention will be more clearly understood when considered in conjunction with the accompanying drawings in which FIGURE 1 is a schematic diagram of one embodiment of the invention,

FIGURE 2 is a detailed schematic preferred embodiment of the invention,

FIGURE 3 is a schematic embodiment of the modification of the invention,

FIGURE 4 is a schematic embodiment of another modiiication of the invention,

FIGURE 5 is a schematic embodiment of another modiiication of the invention,

FIGURE 6 is a schematic embodiment of another form of the invention, and

FIGURE 7 is a schematic embodiment of another form of the invention.

Referring first to FIGURE l, there is illustrated a circuit of one -form of the invention. In this arrangement the load 1 comprising the Hash lamp is connected in parallel with a capacitor or bank of capacitors 2 and in parallel with a sensing element 3. A power supply source 4 is connected in series with a switch 5 in turn connected in series with the elements l, 2 and 3. A compensator 6 is connected across the terminals of the switch 5 and between the terminals of the elements 2 and 3. The sensing element 3 may be a relay which operatively controls the switch 5. The compensator 6 may be a resistance having a high value. The power supply source 4 may be of conventional design providing a voltage in excess of the peak A.C. voltage to which condenser 2 could charge if directly coupled to a conventional A.C. line.

When the potential on capacitor 2 is below a prescribed normal potential, the sensing element 3 maintains switch 5 closed and over-volted power supply 4 then charges the capacitor 2 to said normal potential. As the power supply 4` provides an output voltage greatly in excess vof this normal potential, capacitor 2 is charged thereto in much less time than would be required if the voltage of the source were the same as said normal potential.

When capacitor 2 is charged to this potential, the sensing element 3 causes the switch 5 to open, thereby allowing a current to How to the capacitor only through the compensator 6. As the compensator 6 comprises preferably a resistor of high value, the current flowing through the compensator will be small and of a sufficient value to maintain the selected normal potential level on the capacitor 2. Switching in compensator 6 by opening switch 5 therefore maintains the voltage across the capacitor 2 at substantially the selected normal level once that level is attained.

A system according to the invention can be used to charge a capacitor to a rated value in one-tifth of the time that it takes for normal charging. Thus, assuming circuit parameters in which C equals 2000 mid., R equals 5000 ohms and E equals 450 volts, on the basis of a ten second time constant (RC), the voltage level at various time intervals will be Time Constant: Voltage First (l0 seconds) volts-- `284 Second (20 seconds) do 389 Third (30 seconds) do 4271/2 Fourth (40 seconds) do 442 Fifth (50 seconds) do 450 'former 11 through the lines 12, 13,

Voltage Time Constant:

First seconds) volts 410 Second (20 seconds) do 560 Third (30 seconds) do 6161/2 Fourth (40 seconds) do 638 Fifth (50 seconds) do 650 Thus, Where a power supply is utilized, as in the present invention, with the voltage being in the nature of 11/2 times greater than the prescribed normal voltage, a time saving of approximately one to five may be obtained in charging the capacitor 2 to a level of 450 volts. Cbvious- Yly other parameters may be selected which could also be operative to vary the time constant as desired.

Referring now to FIGURE 2, there is shown a preferred embodiment of the invention. In this arrangement, line power is supplied from a conventional source such as the wall outlet 10 across the primary of the isolating trans- If desired, a signal lamp 14 may be connected across the lines 12, 13. A fuse 15 is in series with the line `13 and a master control switch 16 is in series with the line '12. The secondary ot the isolating transformer is connected with a voltage am- `plier such as the voltage quadrupler 17'. This conventional quadrupler may provide, as for example, an output of 600 volts across its output terminals 18, 19. Connected to the terminals 18, 19 are parallel lines 20, 21, respectively. A switch 22 and contact Z3 are connected in series with the line 20 with the contact 24` connected to Ythe line 25. Switch 22 is adapted to close between con- ,tacts 23, Z4. The line 25 is connected in series with the voltage regulator generally designated Z7, in turn connected in series with the line 26, with the line 26 connected lto the terminal 18 at its other end. When the switch 22 'contacts the contact or terminal 23, poweris applied across the lines 2.0, 21 directly from the voltage quadrupler but when the vswitch is connecte-d to the contact 24, the

through the voltage regulator 27. This voltage regulator 27 may be of conventional design and of a nature such as shown but not specically described within the dotted p outline 27.

A sensing relay 30 operatively controls the switch '22 With this relay being electrically connected across lines `20, 21. This sensing relay may comprisey the coil and .armature 31, which when energized closes the arm 22 to contact 24, in series with a variable resistor 32. A capacitor 34 is connected across the lin-es 20, 21 with a switch and contact 35', 36 in series with capacitor 3ft. A second contact 37 is connected between coil 31 and variable resistor 32 with the switch 35 adapted to close to either the Contact 36 or 37. The capacitor load 38 is connected across the lines 20, 21 and may comprise either a single condenser or a series of parallelly arranged condensers. Also connected across the lines 20 21 is a load in the form of a flash lamp and if desired a safety switch. The load may conventionally be connected to the lines 2.1, Z0 through a cord and socket arrangement. The voltage regulator 27 is connected o n its low side by the line dil to the line 21 at the connection of the capacitive load 38 to the line 21.`

`In the operation of this device, as illustrated in FIG- URE 2, power from the A.C. source 10 is supplied through the isolating transformer, Which is utilized to minimize `the hazard of shock, to the voltage quadrupler 17 which may as noted Yprovide approximately 600 volts across the terminals 18, 19. When the capacitive load 3S has been discharged through the flash lamp load 41 and is again recharging, the se-nsingrelay 30 has closed the switch 2.2 tothe contact 23 and thus there is applied across the lines 20, 21 and consequently across the capacitive load 38, the

saaie 'power from the quadrupler is applied across lines 20, 21

full voltage of the over-volted power supply from the quadrupler 17. This DC. voltage is substantially in excess ofthe normal voltage level maintained on the capacitive load 3S which, for example, may be in the nature of 450 volts. When the voltage across the capacitor reaches the desired level and which may be predetermined by adjusting the resistor 32, the sensing relay 30 will actuate Vcausing the switch 22 to close from the contact 23 to the contact 2111-'. Under these circumstances, lthe power from the voltage quadrupler 17 is applied to the lines 20, 21 through the regulated voltage means Z7 which may, as desired, be selected at 450 volts. The relay voltage for operating the switch 22 and the regulating Voltage should be 'selected at a value as close together as possible. This may be obtained by proper selections of the resistors 42 and d3 in the voltage regulator 27. t

It will benoted that when the switch 22 closes from the contact 23 to the contact 214, there is a short period of time during which moving contact arm is intermediate the contacts 23 and 2d. In order to maintain a voltage across the sensing relay coil 31 and avoid sparking, the capacitor 3d is discharged across this coil 31. The capacitor 34 was previously charged through the contact arm 35 and Contact 36 when the over-volted power supply was connected across the lines 20, 21.A The sensing relay 30 may thus be used to actuate arm 351through its limited distance of travel toward the contact 37 before actuating the contact arm 22. Thus, this capacitor 34 will provide voltage across the coil 31 to `maintain the relay energized until a circuit is closed through the regulated power source.

When the flash lamp is tired, Vthe voltage across the capacitor and sensing device 30 rapidly decreases to a point where the relay coil 31 again operates to move the `contact arm 22 to contact 2.3,thus again completing the dei relatively low voltage system in which the voltage across "the capacitor after it has been charged to its normal voltage and the voltage of the power supply source is normally in the range of perhaps 450 volts.

The embodiment as illustrated in FIGURE 2. discloses one means of providing a sensing element which controls the operating relay and switch 22. It is important, how ever, in some instances to'provide a sensing system which is more precisein its control of the switching from'the unregulated to the regulated power supply. s

In FIGURE 3 a'controlled thyratron tube 50 is connected across the lines 20, 21 withpthe Vcoil of the relay 51 connected to the plate of the thyratron. The relay 51 controls 'the contact arm 22.. The thyratron tube 50 is connected across the lines 21, 2t) in series with the coil 51 yand the resistor 53. A resistor 54 is connected across the line 2d and the cathode of the thyratron 50. Resistors 55 and 56 connected in series across the lines 20, 21 are center tapped to the grid of the thyratron through the resistor 57. A capacitor 5S is connected across the resistor 56. The load 59 is connected across the lines 20, 21. In the operation of this particular circuit, the

thyratron tube 561 is biased by the resistor combination 5'3, 54 which causes the voltage on the cathode of the thyratron to rise above the voltage on the grid to prevent iiring. By properly selecting the parameters of the rresistors 55 and 56 and capacitor 58, the grid voltage on the thyratron may build up until at a specific voltage,

lizes a cathode coupled multivibrator 60 connected between the lines 20, 21. In this circuit, the relay coil 61 is connected to one-half of the tube 63 with that half of the tube biased to cut-off by the resistor 64. At a predetermined voltage determined by the resistors 65, 66 the tube 63 conducts through the relay coil 61 thus actuating the contact arm 22 and throwing it from the unregulated to the regulated power supply. This particular arrangement provides a precise control of the voltage -across the load 68.

In FIGURE there is shown one more means for sensing cut-off Voltage at a precisely desired point. In this arrangement a stabilized voltage reference is utilized for comparison purposes with the voltage as it builds up across the capacitive load. In this arrangement a reference source of voltage obtained by suitable means at 70, such -as a voltage reference tube, is fed into an amplifier 71 together with -a voltage rwhose level is determined by the resistors 72, 73, connected in series across the lines 20, 21. 'Ihe differential amplier 71 controls the thyratron tube 74, being connected to the grid of that tube. A relay coil 75 controlling the switch 22 is connected to the thyratron and when the thyratron is tired at a voltage controlled by the amplifier 71, the relay coil 75 will actuate the contact 22, closing it from the unregulated power supply to the regulated power supply, thus a carefully regulated voltage across the load 76 may be maintained after the capacitor in this load has received its proper and desired charge.

In FIGURE 2, it will be noted there was described an arrangement which included means by which a capacitor 34 was adapted to 4be connected across the coil 31. The purpose of this type of arrangement is to assure proper operation of the switch arm 22 by maintaining a voltage across the relay coil when the arm is travelling between the unregulated power supply. Alternate means are provided which may obtain the same desired results. Such structure is, lfor example, included in the arrangement generally described in FIGURE l, in which power is always supplied across the sensing element through the compensator 6. Such an arrangement is shown in further detail in FIGURE 6. In this arrangement the unregulated and regulated power supplies are connected in parallel with a resistor 80 having a high resistance value in series with the unregulated power supply source. A contact arm 81 is connected in parallel with this resistor 80 and in series with the unregulated power supply. Connected across the lines 20, 21 are a limiting resistor 32 and the coil 83 which actuates and operates the arm 8l. When the load 85 containing the capacitor is being charged, the switch across the resistor 80 is closed, allowing the unregulated power supply to provide most of the charging current to the load. When the cut-off point is reached, the relay coil 83 opens arm 81. Current from the unregulated power supply is then effectively removed due to the large value of the resistance 80 and the regulated power supply is then impressed -across the load.

A still further modilication of this arrangement is shown in FIGURE 7. In this arrangement, the contact arm 22 is adapted to be connected selectively in series With the unregulated or regulated power supply source. Connected across the lines 20, 21 between the unregulated power supply and the contact arm 22 vin series are the relay coil 90, resistor 91, contact arm 492 and line 93. A capacitor 94 is connected in parallel with the relay coil 90, while the contact arm 92 is adapted to close t-he line 93 to the contact 95 or open it to position 96. Also connected across the lines 2li', 21 is the relay coil 97 and the resistor 98 in series wtih it. The load 99 which includes a capacitor `adapted to charge `for subsequent discharge through a fiash bulb, is connected in a manner as previously indicated. In the operation of this particular circuit, when the charging cycle begins, the coil 97 is actuated at a selected voltage causing the arm 92 to close to the contact 95. This occurs in a voltage preferably 6 about Ztl volts lower than the selected voltage to which the load is to be charged. When the contact arm 92 closes to the contact 95, and the coil is thereby actuated, the arm 22 will move from the unregulated to the regulated power supply contact.

Having now described my invention, I claim:

1. A system for rapidly charging and maintaining a voltage level across a capacitive means independent of the capacitive means characteristics adapted to be intermittently discharged, comprising means for charging said capacitive means at an exponential rate toward a desired voltage and means for maintaining the charge on said capacitive means when it has reached substantially said desired voltage comprising a source voltage substantially equal to said desired voltage and means for selectively electrically `disengaging said means for charging and connecting said means for maintaining the charge to said capacitive means when said capacitive means has reached y-said desired voltage.

2. A system as set forth in claimkl wherein said means yfor maintaining the charge comprises a compensator in series with said means -for charging adapted to reduce the source voltage passing through said compensator to substantially said desired voltage and said means for disengaging includes a switch in shunt with said compensator adapted to open when said capacitive means has reached said desired voltage.

3. A system as set forth in claim l wherein said means for disengaging includes a relay having a coil connected substantially in parallel lwith said capacitive means and a switch arm in series with said capacitive means operative when said desired voltage is impressed across said coil Iand adapted to be switched thereby from said means for charging to said means for maintaining the charge.

4. A system as set forth in claim l wherein said means for maintaining the charge includes a voltage regulator for precisely controlling the level `of said desired voltage.

5. A system as set forth -in claim 3 wherein means are provided for maintaining substantially said desired voltage across said coil when said switch arm is being actuated.

6. Apparatus for rapidly charging a capacitor to a selected voltage level and maintaining it there, comprising a first source of an output voltage substantially in excess of said selected voltage level, a second source of an output voltage substantially equal to said selected Voltage level, and means dependent on the voltage level of said capacitor to effectively :transfer the latter from` said first source to said second source dur-ing the charging period.

7. Apparatus for rapidly charging a capacitor to its rated voltage level and maintaining it there, comprising a first source of unregulated voltage substantially in excess of said rated Voltage level, a second source of regulated voltage substantially equal to said related voltage level, and switching means dependent on the voltage level of said capacitor to effectively transfer the latter from said iirst source to said second source during the charging period.

8. Apparatus for rapidly charging a capacitor toi its rated voltage level and maintaining it there, comprising first means adapted to apply a voltage to said capacitor substantially in excess of said rated level, second means adapted to apply a voltage to said capacitor substantially equal to said rated level, means for sensing the voltage level of said capacitor, and switching means actuated by said sensing means adapted to transfer said capacitor from said first means to said second lmeans during said charging period.

9. The apparatus of claim 8 wherein means are provided for maintaining a voltage across said sensing means during the transfer of said capacitor by switching.

l0. The apparatus of claim 8 and further comprising additional switching means for maintaining a connection during said charging period between said capacitor and one of said means for applying a voltage thereto.

7 i 11. The apparatus of claim 8 wherein said irst and second means for applying a voltage respectively comprise unregulated `and regulated power sources.

Y 12. The apparatus of claim 11, and further comprising means for maintaining la'connection during said charging period between Ysaid capacitor land one of said means for applying a voltage thereto.

13. The apparatus of claim 11 wherein said sensing means comprises a relay connected in series with an electron tube.

14. A system as set forth in claim 6, wherein said voltage dependent means includes a thyr-atron tube adapted to iire yat a selected voltage with a relay controlling `said connecting means electrically coupled to the plate of `said tube. Y

15. A system as set forth in claim` 6, wherein said volt age dependent means includes 4a cathode coupled multivibrator adapted to actuate said means 'for connecting said capacitive means. v Y

16. Apparatus for rapidly charging a capacitive load to a prescribed voltage level'comprising, a lfirst terminal 'normally maintained at -a potential much greater than said prescribed voltage level, a second terminal normally maintained at said prescribed voltage level, and switching means responsive to the potential across said capacitive load for selectively connecting said first terminal to said load While the voltage thereacross lis less than said pre* scribed voltage level and connecting `said second terminal to said load `after said level is attained to normally maintain said capacitive load `charged vtoV said prescribed voltage level.

References Cited in the file of this patent UNITED STATES PATENTS 2,102,883 Bouwers v Dec. 2l, 1937 2,250,102 Klemperer July 22, 1941 2,383,492 Klemperer Aug. 28, 1945 2,385,736 Smith et al. Sept. 25., 1945 2,468,080 VKlemperer ,Aprl 26, 1949 v 2,771,575 Hampton Nov. 20, 1956 2,891,209 Schalk lune 16, 1959 

